Method and Device for Testing the Measuring Value of at Least One Level Sensor Arranged in a Fuel Tank

ABSTRACT

Disclosed is a method for checking for errors in the measured value or values of one or more filling level sensors arranged in a fuel tank of a motor vehicle, characterized in that the measured values of a plurality of measurements are sensed and are each compared with a further physical variable for plausibility. If the measured values are not plausible, a warning signal is fed to a warning device and a warning information item is triggered by the warning device.

BACKGROUND OF THE INVENTION

Method and device for testing the measuring value of at least one level sensor arranged in a fuel tank.

The invention relates to a method for checking for faults in the measured value or values of one or more filling level sensors arranged in a fuel tank of a motor vehicle. Defects in the filling level sensors can lead to an incorrect display of the contents of the fuel tank. This entails the risk of the motor vehicle becoming immobile as a result of an empty fuel tank, which is particularly dangerous if this occurs on a freeway.

When there are a plurality of filling level sensors, such as is the case for example in saddle-type fuel tank systems with a plurality of chambers of the fuel tank, the risk of an incorrect display of the contents of the fuel tank is higher the greater the number of filling level sensors.

The object of the invention is therefore a method and a device for carrying out the method of the type mentioned at the beginning by which the fault or faults of the filling level sensor or sensors can be detected.

This object is achieved according to the invention in that the measured values of a plurality of measurements are sensed and are each compared with a further physical variable for plausibility, and in that if they are not plausible a warning signal is fed to a warning device and a warning information item is triggered by the warning device.

As a result of this design, a warning information item is issued immediately after it has been determined that the values are not plausible. The acquisition of a plurality of measurements avoids the possibility of a warning being issued if just one of the plurality of measurements is not plausible but the other measurements are plausible.

The plurality of measurements preferably take place within a specific time period.

A measurement interval with the plurality of measurements can each be triggered after expiry of a specific operating time of the engine or by means of a specific operating function of the motor vehicle.

Such a specific operating function can be the switching on or the switching off of the ignition or an idling mode of the engine.

It is thus not necessary to carry out monitoring continuously but rather only on specific occasions.

In order to acquire the measured values of a plurality of measurements when there is a fuel tank having a plurality of chambers, the measured values of the filling level sensors which are arranged in the chambers are summed and the sum of measured values is compared with the further physical variable for plausibility.

One possibility for a physical variable for determining the plausibility is for the further physical variable to be the value of a quantity of fuel which is extracted from the fuel tank by a fuel pump and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.

In another possibility, the physical variable can be the value of the quantity of fuel which is injected into the engine of the motor vehicle by an injection system and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.

No further measured values are supplied and it is thus particularly easy that the further physical variable is the measured value of a measurement or the measured value of a plurality of the measurements which, for the determination of the plausibility, yield approximately constant values when they are compared with one another.

The warning information item can be a visual and/or an audible warning information item.

In order to reliably avoid displaying a larger value for the contents of a fuel tank than is actually present, the warning signal can trigger the display of an empty fuel tank on a filling level display.

However, it can also switch on a fault information display.

The second part of the object is achieved with a device for carrying out the method by virtue of the fact that a filling level sensor is arranged in a fuel tank, the measured values of which sensor can be fed to a computer unit and can be compared with one or more measured values of one or more measured values which are determined previously, the computer unit being able to generate a warning signal if the measured value deviates from the previously determined measured values.

This object is also achieved by virtue of the fact that the at least two filling level sensors are arranged in a fuel tank, the measured values of which sensors can be fed to a computer unit and can be summed by the computer unit to form a measured value sum, and can be compared with a measured value sum, of one or more previously determined measured value sums, the computer unit being able to generate a warning signal if the measured value sum deviates from the previously determined measured value sums.

The computer unit can at the same time be used for actuating a filling level display which can display a filling level corresponding to the measured value sum.

One possibility for the warning information item is that a fault information display can be actuated by the warning signal.

However, it is also possible for the filling level display to be actuated by the warning signal.

This can be done, for example, by the filling level display displaying the filling level zero or being actuated so as to flash.

A particularly advantageous application is that the fuel tank is a fuel tank which has a plurality of fuel chambers, at least one filling level sensor being arranged in each chamber.

One of the chambers can be a main chamber and the other chambers can be secondary chambers, a fuel pump by which fuel can be delivered to an internal combustion engine being arranged in the main chamber.

If pumps by which fuel can be delivered from the secondary chambers into the main chamber are arranged in the secondary chambers, a plausibility check is nevertheless possible since the measured value sum of measured values of all the filling level sensors is always formed.

One simple and cost-effective embodiment of the pumps is possible by virtue of the fact that the pumps are suction jet pumps which can be driven by a branch of the delivery current of the fuel pump.

If the fuel pump can be open-loop or closed-loop controlled by the computer unit, only corresponding programming of the computer unit but no separate electronics is required.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention is illustrated in the drawing and will be described in more detail below. In the drawing:

FIG. 1 is a basic illustration of a fuel tank system for a motor vehicle with a fuel tank which has a plurality of chambers, and

FIG. 2 is a block circuit diagram of a device for carrying out a method for checking the measured values of the filling level sensors of the fuel tank system according to FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The fuel tank system illustrated in FIG. 1 has a fuel tank 1 which is embodied as saddle-type tank with two chambers, one chamber being a main chamber 2 and the other chamber being a secondary chamber 3.

In the main chamber 2 there is a surge pot 4 in which a delivery unit 5 with a fuel pump 6 which sucks in fuel from the surge pot 4 and delivers it via a pressure regulator 7 to an injection system (not illustrated) of a motor vehicle is arranged.

The fuel which is decreased by the pressure regulator 7 is fed back into the surge pot 4.

A branch 8 of the delivery current leads off from the delivery unit 5, and, on the one hand, a part of said branch 8 is fed to a first suction jet pump 9 and operates it, the suction jet pump sucking in fuel from the main chamber 2 and delivering it into the surge pot 4.

Another part of the branch 8 of the delivery current is fed into the secondary chamber 3 and operates a second suction jet pump 10 there. This second suction jet pump 10 delivers fuel from the secondary chamber into the surge pot 4.

In the main chamber 2, a first filling level sensor 11 for sensing the respective filling level N 1 is arranged in the main chamber 2 and a second filling level sensor 12 for sensing the respective filling level N 2 in the secondary chamber 3 is arranged in the secondary chamber 3.

According to the block circuit diagram illustrated in FIG. 2, the measured values of the filling level sensors 11 and 12 are supplied to a computer unit 16 via data lines 13 and 14 and via an input unit 15.

In the computer unit 16, the measured values of the two filling level sensors 11 and 12 are summed to form a measured value sum, and a corresponding filling level signal is supplied for actuating a filling level display 17 which, after previous attenuation and averaging, can be arranged in a display panel of the motor vehicle and displays the overall filling level of the fuel tank 1.

Furthermore, for example five measured value sums which are determined at brief time intervals in succession are stored in the computer unit 16 and the last measured value sum determined is compared with the four previously determined measured value sums.

However, the five measured value sums can also be compared with one another.

If at least the majority of the measured value sums which are compared with one another are approximately the same, the computer unit 16 detects the measured value sums as being plausible. This means that the filling level sensors 11 and 12 and the means of transmitting their measured values to the computer unit are satisfactory.

An absolute identity of the measured value sums is not necessary since splashing effects of the fuel due to dynamic driving movements affect the measured value. Furthermore, the quantity of fuel which is required for the injection system also has an effect. The measured value sums must therefore be located only within a tolerance band in order to be considered identical by the computer unit 16.

If the majority of the measured value sums which are compared with one another are not approximately the same, the computer unit 16 generates a warning signal and supplies it to a fault information display 18 and actuates the latter.

At the same time, the filling level display 17 can be actuated by the computer unit 16 in such a way that it displays an empty fuel tank 1.

This indicates that either one or both filling level sensors 11 and 12 or their means of transmitting measured values to the computer unit 16 are not satisfactory. 

1. A method for checking for errors in the measured value or values of one or more filling level sensors arranged in a fuel tank of a motor vehicle, characterized in that the measured values of a plurality of measurements are sensed and are each compared with a further physical variable for plausibility, and in that if they are not plausible a warning signal is fed to a warning device and a warning information item is triggered by the warning device.
 2. The method as claimed in claim 1, characterized in that the plurality of measurements take place within a specific time period.
 3. The method as claimed in claim 2, characterized in that the measurements are each triggered after expiry of a specific operating time of the engine of the motor vehicle.
 4. The method as claimed in claim 2, characterized in that the measurements are triggered by a specific operating function of the motor vehicle.
 5. The method as claimed in claim 3, characterized in that the specific operating function is the switching on or the switching off of the ignition or an idling mode of the engine.
 6. The method as claimed in claim 1, characterized in that when there is a fuel tank (1) having a plurality of chambers the measured values of the filling level sensors (11, 12) which are arranged in the chambers are summed and the sum of measured values is compared with the further physical variable for plausibility.
 7. The method as claimed in claim 1, characterized in that the further physical variable is the value of a quantity of fuel which is extracted from the fuel tank by a fuel pump and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.
 8. The method as claimed in claim 1, characterized in that the further physical variable is the value of the quantity of fuel which is injected into the engine of the motor vehicle by an injection system and which, for the determination of the plausibility, yields an approximately constant value when added to the measured value or values of the filling level sensors for at least a plurality of the measurements.
 9. The method as claimed in claim 1, characterized in that the further physical variable is the measured value of a measurement or the measured values of a plurality of the measurements which, for the determination of the plausibility, yield approximately constant values when they are compared with one another.
 10. The method as claimed in claim 1, characterized in that the warning information item is a visual and/or an audible warning information item.
 11. The method as claimed in claim 10, characterized in that the warning signal triggers the display of an empty fuel tank (1) on a filling level display (17).
 12. The method as claimed in claim 10, characterized in that the warning signal switches on a fault information display (18).
 13. A device for carrying out the method as claimed in claim 1, characterized in that a filling level sensor is arranged in a fuel tank, the measured values of which sensor can be fed to a computer unit and can be compared with one or more measured values of one or more measured values which are determined previously, the computer unit being able to generate a warning signal if the measured value deviates from the previously determined measured values.
 14. A device for carrying out the method as claimed in claim 1, characterized in that at least two filling level sensors (11, 12) are arranged in a fuel tank (1), the measured values of which sensors (11, 12) can be fed to a computer unit (16) and can be summed by the computer unit (16) to form a measured value sum, and can be compared with a measured value sum of one or more previously determined measured value sums, the computer unit (16) being able to generate a warning signal if the measured value sum deviates from the previously determined measured value sums.
 15. The device as claimed in claim 14, characterized in that the computer unit (16) can actuate a filling level display (17) which can display a filling level corresponding to the measured value sum.
 16. The device as claimed in claim 15, characterized in that a fault information display (18) can be actuated by the warning signal.
 17. The device as claimed in claim 15, characterized in that the filling level display can be actuated by the warning signal.
 18. The device as claimed in claim 14, characterized in that the fuel tank (1) is a fuel tank which has a plurality of fuel chambers, at least one filling level senor (11, 12) being arranged in each chamber.
 19. The device as claimed in claim 18, characterized in that one of the chambers is a main chamber (2) and the other chambers are secondary chambers (3), a fuel pump (6) by which fuel can be delivered to an internal combustion engine being arranged in the main chamber (2).
 20. The device as claimed in claim 19, characterized in that pumps by which fuel can be delivered from the secondary chambers (3) into the main chamber (2) are arranged in the secondary chambers (3).
 21. The device as claimed in claim 20, characterized in that the pumps are suction jet pumps (9, 10) which can be driven in particular by a branch (8) of the delivery current of the fuel pump (6).
 22. The device as claimed in claim 19, characterized in that the fuel pump (6) can be open-loop or closed-loop controlled by the computer unit (16). 